Three chamber load lock apparatus

ABSTRACT

A functional load lock apparatus having two or more load lock chambers mounted on a central chamber which can be mounted on a single opening in a vacuum chamber such as a substrate processing platform for making integrated circuits on silicon wafers. Each load lock chamber preferably has a semi-cylindrical valve which remains sealed when the load lock chamber is open to atmospheric pressure. A wafer cassette holder positioned within each load lock chamber can be loaded and unloaded while the semi-cylindcical valves seal the vacuum chamber from atmospheric pressure. The semi-cylindrical valve pivots to an open position when the load lock chamber is under vacuum and the entire wafer cassette moves from the load lock chamber to the central chamber.

This is a continuation of application Ser. No. 08/746,859 filed on Nov.18, 1996, now U.S. Pat. No. 5,961,269, issued Oct. 5, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to loading and unloading of vacuumchambers while a vacuum is maintained in the chamber. More specifically,the invention relates to a load lock apparatus for loading siliconsubstrates in a substrate processing platform.

2. Background of the Related Art

Cluster tools which combine numerous substrate processing units in aprocessing platform have become generally accepted as an effective andefficient concept in advanced microelectronics manufacturing. A clustertool generally refers to a modular, multi-chamber, integrated processingsystem. It typically consists of a central wafer handling vacuum chamberand a number of peripheral vacuum process chambers. The silicon wafersgo through a set of process steps under vacuum in the various processstations without being exposed to ambient conditions. The transfer ofthe wafers for the processes is managed by the wafer handling vacuumchamber which is also maintained under vacuum conditions. Cluster toolsoffer significantly higher yields on account of lower defect densities.Different types of cluster tools, such as linear or radial, withdifferent types of architecture are possible.

Substrate processing platforms typically include at least two load lockchambers mounted on separate openings in the central wafer handlingvacuum chamber for loading or unloading silicon wafers while the vacuumchamber remains under vacuum. The load lock chambers occupy valuablepositions on the processing platform which would otherwise be used foradditional process chambers. However, two chambers are usually requiredto maintain continuous operation such that wafers are processed from oneload lock chamber while finished wafers are unloaded from the otherchamber and new wafers are loaded.

FIG. 1 (prior art) shows a commercially available substrate processingplatform offered by Applied Materials, Inc. under the trademark Endura®.The platform combines vacuum chambers designed to process silicon wafersat low/high pressure vacuum in the range of 10⁻³ to 10⁻⁸ torr.

Referring to FIG. 1, silicon wafers in a cassette 10 are introduced andwithdrawn from the platform 52 through a first slit valve by a firstload lock chamber 12 or through a second slit valve by a second loadlock chamber 14. A fist robot 16 having a blade 18 is located in abuffer chamber 20 to move a wafer 22 between various chambers 24, 26, 28surrounding the buffer chamber 20. A second robot 30 is located in atransfer chamber 32 to transfer a wafer 34 between various chambers 28,36 surrounding the transfer chamber 32. The buffer chamber 20 and thetransfer chamber 32 are connected through two common chambers 28. It isunderstood in the art that a wafer may be processed or cooled in one ormore chambers for any number of times in any order to accomplishfabrication of a desired semiconductor structure on the wafer. Amicroprocessor controller 38 and associated software is provided tocontrol processing and movement of wafers.

Attempts to connect two or more load lock chambers to a single slitvalve in a processing platform have been unsuccessful. Such an apparatusmust have internal valves large enough for the transfer of entirecassettes of wafers. Large valves are difficult to seal when the loadlock chamber is open to the atmosphere and is mounted on a chamber thatis under high vacuum.

It is an objective of the present invention to provide a load lockapparatus for mounting two load lock chambers on a single slit valve ina substrate processing platform. It is a further objective of thisinvention to provide a large valve in a load lock chamber which willremain sealed when the load lock chamber is mounted on an opening in avacuum chamber under high vacuum conditions.

SUMMARY OF THE INVENTION

The present invention provides a functional load lock apparatus havingtwo or more load lock chambers mounted on a central chamber which can bemounted on a single opening in a vacuum chamber such as a substrateprocessing platform for making integrated circuits on silicon wafers.

The present invention also provides a load lock apparatus having asemi-cylindrical valve mounted in a load lock chamber. Thesemi-cylindrical valve remains sealed when the load lock chamber is opento atmospheric pressure. A wafer cassette holder positioned within eachload lock chamber can be loaded and unloaded while the semi-cylindricalvalves seal the vacuum chambers from atmospheric pressure. Thesemi-cylindrical valve pivots to an open position when the load lockchamber is under vacuum and the entire wafer cassette moves from theload lock chamber to the central chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features, advantages and objects of thepresent invention can be understood in detail, a more particulardescription of the invention, briefly summarized above, may be had byreference to the embodiments thereof which are illustrated in theappended drawings.

The appended drawings illustrate typical embodiments of this inventionand are not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

FIG. 1 (prior art) is a top schematic view of a radial cluster tool forbatch processing of silicon wafers.

FIG. 2 is a front schematic view of a load lock apparatus of the presentinvention comprising two load lock chambers for mounting to a slit valvein a substrate processing platform such as the radial cluster tool ofFIG. 1;

FIG. 3 is a side schematic view of the load lock apparatus of FIG. 2.

FIG. 4 is a side sectional view of the load lock apparatus of FIG. 2showing internal semi-cylindrical valves;

FIG. 5 is a rear sectional view of the load lock apparatus of FIG. 2showing the internal semi-cylindrical valve and wafer cassettes;

FIGS. 6-9 are top sectional views of the load lock apparatus of FIG. 2;

FIGS. 10-12 are sectional views of a load lock chamber of the load lockapparatus of FIG. 2 showing movement of the semi-cylindrical valve;

FIGS. 13-15 are detail views of the semi-cylindrical valves includingseparate valve seals; and

FIG. 16 is a top schematic view of the load lock apparatus of FIG. 2replacing both of the load lock chambers on the cluster tool of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides a load lock chamber having atwo or more isolatable regions selectively communicable with a centraltransfer region. The load lock chamber is preferably mounted on a vacuumsystem so that the central transfer region is selectively communicablewith the vacuum system. Each load lock region defines a loading portdisposed in a sidewall and includes a door valve mounted in the loadingport and a transfer port selectively communicable with the transferregion. A valve is rotatably disposed in each region to selectivelycommunicate each load lock region with the transfer region. The centralhousing of the loadlock chamber preferably includes a transfer portwhich is selectively communicable with the vacuum system and a portselectively communicable with each load lock region so that wafers canbe moved from each load lock region into the transfer region and theninto the vacuum system.

In one embodiment of the present invention, a sealing valve is disposedin each load lock region to selectively communicate the load lock regionand the transfer region. Preferably, the valve is a semi-cylindricalvalve rotatably disposed in the load lock region. A wafer cassetteholder is mounted on a shaft which is movably disposed in each load lockregion to move the wafer cassette into the transfer region. An elevatormechanism, such as a stepper motor, moves the cassette holder within theload lock region to transfer the wafer cassette holder between the loadlock region and the central transfer region. In one embodiment, at leasttwo load lock housings are mounted on a central housing to eliminate theneed for a second load lock chamber mounted on a separate opening in thevacuum chamber.

The load lock chamber of the present invention is preferably operated bya microprocessor controller provided with the vacuum system. Thesequence and timing of operating the load lock chamber is provided sothat a first load lock region is loaded and pumped down to a selectedpressure so that a wafer cassette can be moved into the transfer regionand wafers moved into the vacuum system. While the wafers are beingprocessed, the second load lock region is loaded and pumped down to thedesired pressure. After the wafers moved from the first region areprocessed, the wafer cassette is moved back into the load lock regionand the valve disposed between the transfer region and the load lockregion is closed. The wafer cassette in the second load lock region isthen moved into the transfer region and the wafers loaded into thesystem.

A preferred load lock apparatus for mounting on a vacuum system havingtwo or more load lock chambers which have semi-cylindrical valvesdisposed in the ports located between the load lock chambers and are thecentral transfer chamber will be described in references to FIGS. 2-15.The various chamber components are preferably machined from aluminum,but may be comprised of any other material known in the art andcompatible with vacuum processing.

FIG. 2 is a front view of a preferred load lock apparatus of the presentinvention comprising two load lock chambers for mounting to a slit valvein a substrate processing platform such as the radial cluster tool ofFIG. 1. The load lock chambers are preferably vertically aligned arounda central chamber to make room for processing chambers on adjacent slitvalves. Referring to FIG. 2, the load lock apparatus 40 comprises acentral housing 42 having a slit 48 for mounting adjacent a slit valveon a processing platform The slit 48 will usually have a widthcorresponding to passage of a silicon wafer. However, the use of doublewide slits for passage of two wafers side-by-side is also contemplated.Each substrate cassette holder 60, 104 (shown in FIG. 5) may support twosubstrates in a side-by-side relationship. The central housing 42 has avacuum port 54 for connection to a vacuum system commonly provided withthe processing platform 52 or optionally provided with the load lockapparatus.

The load lock apparatus further comprises a first load lock housing 56mounted on the central housing 42. A door valve 66 having external knobs68 which engage the first load lock housing 56 provide access forloading and unloading wafers as described for FIG. 5 below. Preferably,the door valve 66 is operated automatically by the processing platform.Automatic door valves are used commercially on the load lock chambers ofFIG. 1 and can be included on the present invention. A vacuum port 70 onthe first load lock housing 56 connects to a vacuum system commonlyprovided with the processing platform 52 or optionally provided with theload lock apparatus. The vacuum system typically can achieve pressureslower than 0.01 Torr in a load lock chamber.

Rotatable seals 76 are mounted in both sides of the load lock housing 56and pivot pins 82 are rotatably mounted in the rotatable seals 76.Pneumatic actuating arms 78 are externally fastened at one end to theload lock housing 56 and the other ends are pivotally linked to pivotarms 80 which are fastened to the pivot pins 82. External components ofa first cassette elevator 90 are protected by a shield 98 which ismounted on the load lock housing 56 and also secures an end of thepneumatic actuating arms 78. Expansion or contraction of the pneumaticactuating arms 78 rotates the pivot pins 82 and operates internalcomponents as described for FIG. 4 below.

The first cassette elevator 90 moves a cassette of wafers within theapparatus as described for FIG. 5 and externally includes a shaft 92which slides through a packing gland 94 mounted on the load lock housing56.

The load lock apparatus 40 further comprises a second load lock housing100 mounted on the central housing 42. A door valve 110 having knobs 112which engage the second load lock housing 100 provide access for loadingand unloading wafers as described for FIG. 5 below. Preferably, the doorvalve 110 is operated automatically by the processing platform 52 asdescribed above. A vacuum port 114 on the second load lock housing 100connects to a vacuum system as described for the vacuum port 70 on thefirst load lock housing 56.

The load lock apparatus further comprises rotatable seals 120 and pivotpins 126 on the second load lock housing 100 as described for the firstload lock housing 56. Pneumatic actuating arms 122 are fastened to theload lock housing 100 at one end and the other ends are linked to pivotarms 124 which are fastened to the pivot pins 126. External componentsof a second cassette elevator 130 are protected by a shield 138 which ismounted on the load lock housing 100 and also secures an end of thepneumatic actuating arms 122. Expansion or contraction of the pneumaticactuating arms 122 rotates the pivot pins 126 and operates internalcomponents described for FIG. 4 below.

The second cassette elevator 130 moves a second cassette of waferswithin the apparatus as described for FIG. 5 and externally includes ashaft 132 which slides through a packing gland 134 mounted on the secondload lock housing 100.

FIG. 3 is a side view of the load lock apparatus of FIG. 2 and shows thefirst pneumatic arms 78 in an extended position for comparison to aretracted position shown for the second pneumatic arms 122.

FIG. 4 is a side sectional view of the load lock apparatus of FIG. 2showing internal chambers and semi-cylindrical valves. The centralhousing 42 internally comprising first 44 and second 46 openings and theslit 48 for transferring substrates between a central chamber 50 withinis the central housing and the processing platform 52. The first loadlock housing 56 internally comprising a first opening 58 adjacent thefirst opening 44 of the central housing 42 for transferring a firstsubstrate cassette holder 60 (FIG. 5) between the central chamber 50 anda first load lock chamber 62 within the first load lock housing 56. Thefirst load lock housing 56 further comprises a second opening 64 forloading or unloading the first substrate cassette holder 60 through thedoor valve 66.

The load lock apparatus 40 internally comprises a first semi-cylindricalvalve 72 pivotally mounted to the first load lock housing 56. Thesemi-cylindrical valve 72 is fastened by screws or the like at each sideto flexible brackets 74 which are fastened to eccentric supports 75.Each eccentric support 75 is fastened to one of the pivot pins 82 whichpass through the load lock housing 56 as described for FIG. 2. Expansionor contraction of the pneumatic actuating arms 78 rotates the eccentricsupports 75 and moves the semi-cylindrical valve 72 between an openposition and a closed position to selectively communicate the first loadlock chamber 62 and the central chamber 50. Connection of thesemi-cylindrical valve 72 to the load lock housing 56 can be achieved ina variety of ways. The flexible brackets 74, eccentric supports 75, androtatable seals 76 shown in FIG. 4 minimize vacuum leaks while m m gwear of internal valve components in the load lock chamber 62.

The second load lock housing 100 internally comprises a first opening102 adjacent the second opening 46 of the central housing 42 fortransferring a second substrate cassette holder (FIG. 5) between thecentral chamber 50 and a second load lock chamber 106 within the secondload lock housing 100. The second load lock housing 100 furthercomprises a second opening 108 for loading or unloading the secondsubstrate cassette holder 104 through the door valve 110.

The load lock apparatus further comprises a second semi-cylindricalvalve 116 pivotally mounted to the second load lock housing 100 byflexible brackets 118, eccentric supports 119, pivot pins 126, androtatable seals 120 as described for the first semi-cylindrical valve72. The semi-cylindrical valve 116 has the same valve stops 83 and thesame movement (FIGS. 10-12) described for the first semi-cylindricalvalve 72.

FIG. 5 is a rear sectional view of the load lock apparatus of FIG. 2showing the internal semi-cylindrical valves and wafer cassettes. Thefirst semi-cylindrical valve 72 is removed from the drawing to show asemi-cylindrical surface 88 on the first load lock housing 56 forseating the first semi-cylindrical valve. The load lock apparatus 40further comprises the first cassette elevator 90 mounted to the firstsubstrate cassette holder 60 for moving the first substrate cassetteholder between the first load lock chamber 62 and the central chamber50. The first cassette elevator 90 can be any means for moving thecassette holder 60 such as the shaft 92 which slides through the packinggland 94 mounted on the load lock housing 56. Preferably, the shaft 92engages a screw drive system 96FIG. 3) which aligns the cassette holder60 with the slit 48 in the central chamber 50.

The load lock apparatus 40 further comprises the second cassetteelevator 130 mounted to the second substrate cassette holder 104 formoving the second substrate cassette holder between the second load lockchamber 106 and the central chamber 50. The second cassette elevator 130can be any means for moving the cassette holder 104 such as the shaft132 which slides through the packing gland 134 mounted on the load lockhousing 100. Preferably, the shaft 132 engages a screw drive system 136(FIG. 3).

Each substrate cassette holder 60, 104 may have individual slits forreceiving wafers or optionally may house an external wafer cassettewhich slips into the substrate cassette holder to accelerate loading andunloading. Each cassette elevator 90, 130 is vertically indexable sothat every substrate in each substrate cassette holder 60, 104 can bedelivered by the first robot 140 through the slit 48 in the centralhousing 42. For example, computer-controlled, stepper motor-driven leadscrew drive systems 96, 136 may be used to position the substratecassette holders 60, 104 for loading and unloading wafers through thedoor valves 66, 112 in each load lock housing 42, 100 and for loadingand unloading wafers through the slit 48 in the central housing 42. Thescrew drive systems are currently used to perform the same function onthe commercially available platform of FIG. 1.

FIGS. 6-9 show horizontal cross-sections through chambers inside theload lock apparatus as indicated in FIG. 5. FIG. 6 shows a cross-sectionthrough the first load lock chamber 62 looking toward thesemi-cylindrical surface 88 on the first load lock housing 56. The viewalso shows the first opening 58 in the first load lock housing 56 andthe valve stops 83. FIG. 7 show a cross-section through the centralchamber 50 looking toward the first opening 102 in the second load lockhousing 42. FIG. 8 is a cross-section through the second load lockchamber 106 and the shaft 132 which mounts the second substrate holder104. FIG. 9 is a cross-section through the shaft 132 looking toward thepacking gland 134 outside the second load lock housing 100.

FIGS. 10-12 show the movement ofthe first semi-cylindrical valve 72.Rotation of the pivot pins 82 also rotates the eccentric supports 75which mount the flexible brackets 74 and the semi-cylindrical valve 72.Initial rotation of the pivot pins 42 moves the semi-cylindrical valve72 from an open position, FIG. 10, to a closed position, FIG. 11,wherein the flexible brackets 74 are blocked by the valve stops 83.Further rotation of the pivot pins 82 causes the flexible brackets 74 toflex away from the eccentric supports 75 and push the semi-cylindricalvalve 72 outward to contact the semi-cylindrical surface 88 on the loadlock housing 56. Venting of the load lock chamber 62 to atmosphericpressure pushes the semi-cylindrical valve 72 tighter toward thesemi-cylindrical surface 88. Thus, the high pressure differentialbetween the load lock chamber 62 and the central chamber 50 during waferloading and unloading makes a tighter seal around the semi-cylindricalvalve 72 and assists in sealing the central chamber 50. Thesemi-cylindrical valve 72 is not moved while a pressure differentialexists between the central chamber 50 and the load lock chamber 62. Thesemi-cylindrical valve 72 is opened after the load lock chamber 62 isevacuated to about the same vacuum as the central chamber 50. Retractionof the pneumatic arms 78 opens the semi-cylindrical valve 72 by pullingthe semi-cylindrical valve 72 away from the semi-cylindrical surface 88on the load lock housing 56.

FIGS. 13-15 are detail views of the semi-cylindrical valves showingdetachable valve seals which can be replaced when worm. FIG. 13 is apartial section view of the semi-cylindrical valve 72 showing theflexible brackets 74 supporting each end of the semi-cylindrical valve.The semi-cylindrical valve 72 preferably has a detachable seal 84 whichis formed by machining channels in both sides of a flat aluminum sheetand rolling the sheet to the desired shape. Durable elastomer seals 86,such as VITON fluoroelastomer (a trademark of du Pont), are adhered tothe channels in the detachable seal 84. The outer elastomer seal 86rests against the semi-cylindrical surface 88 around the first opening58 in the first load lock housing 56. The inner elastomer seal 86 ispreferably the same as the outer seal, but could be an 0-ring which isnot adhered to the channel in the detachable seal 84. FIG. 14 is across-section through the detachable seal 84 and elastomer seals 86.FIG. 15 is a plane view of the detachable seal 84 showing that theelastomer seal 86 is positioned near the perimeter of the detachableseal 84.

FIG. 16 shows the load lock apparatus 40 of the present inventionmounted on the commercially available substrate processing platform 52of FIG. 1. A first robot 140 having a blade 142 is located in a bufferchamber 144 to move a wafer 146 between various chambers 150, 152, 154surrounding the buffer chamber 144. A second robot 160 is located in atransfer chamber 162 to transfer a wafer 164 between various chambers154, 166 surrounding the transfer chamber 162. The buffer chamber 144and the transfer chamber 162 are connected through two cooling chambers154. It is understood in the art that a wafer may be processed or cooledin one or more chambers for any number of times in any order toaccomplish fabrication of a desired semiconductor structure on thewafer. A microprocessor controller 180 and associated software controlsmovement and processing of wafers throughout the system.

Alternative means for connecting the semi-cylindrical valves 72, 116 tothe first and second load lock housings 56, 100 include rigid bracketsthat are fastened to the semi-cylindrical valves and to the pivot pins82, 126 without the eccentric supports 75, 119. Pushing or pulling thesemi-cylindrical valves with respect to the semi-cylindrical surfaces 88on the load lock housings 56, 100 can be accomplished with a rigidbracket by eccentrically mounting the pivot pins 82, 126 in therotatable seals 76, 120 and fastening external levers to the rotatableseals. When the cylinder valves are in a closed position, the externallevers are separately actuated to rotate the seals and shift the pivotpins toward the semi-cylindrical surfaces 88. As another alternative,the flexible brackets 74, 118 could be replaced by hinged brackets thatare spring biased in a retracted position when the valves are open.Rotation of the hinged brackets will also be blocked by the valve stops83 and continued rotation of the pivot pins 82, 126 will straighten thehinged bracket and push the semi-cylindrical valve against thesemi-cylindrical surface 88.

Operation of the load lock apparatus 40 is very similar to operation oftwo separate load lock chambers 12, 14 after the load lock apparatus 40has been mounted on the substrate processing platform 52. The centralchamber 50 is preferably connected by vacuum port 54 to the vacuumsource provided with the platform 72. The vacuum port 54 is used toevacuate the central chamber 50 in the load lock apparatus 40, but maybe used to evacuate the entire buffer chamber 144 in the platform 72.The central chamber 50 will typically be purged with dry nitrogen toremove moisture and evacuated to a pressure below 0.01 Torr while bothsemi-cylindrical valves 72, 116 are closed. The load lock chambers 62,106 are also purged with dry nitrogen while the central chamber 50 ispurged and evacuate& The central chamber 50 is generally maintained atthe same conditions as the buffer chamber 144 during all process steps.

After the central chamber 50 is evacuated, the semi-cylindrical valves72, 116 tightly seal the central chamber 50 and purging of the firstload lock chamber 62 can continue while wafers are loaded in the firstsubstrate cassette holder 60. The first door valve 66 is then closed andthe first load lock chamber 62 is evacuated through vacuum port 70 to apressure less than 0.01 Torr. The first semi-cylindrical valve 72 isthen opened and the first cassette mover 90 moves the first substratecassette holder 60 into the central chamber 50.

While wafers in the first substrate cassette holder 60 are beingprocessed in the platform 52, the wafer loading procedure is repeatedfor the second substrate cassette holder 108 in the second load lockchamber 106. After all wafers in the first substrate cassette holder 60have been returned from the platform 52, the first cassette holder 60 isreturned to the first load lock chamber 62, the first semi-cylindricalvalve 72 is closed, and the first load lock chamber 62 may be vented andpurged with a gas such as dry nitrogen. The second door valve 110 isthen closed and the second load lock chamber 106 is evacuated throughvacuum port 114 to a pressure below 0.01 Torr. Wafers in the secondsubstrate cassette holder 104 are then moved into the central chamber 50and processed in the platform 52 while processed wafers are removed fromthe first cassette holder 60.

Operation of the platform 52 continues until all wafers in the secondsubstrate cassette holder 104 are processed and returned to the cassetteholder 104. The second cassette holder 104 is returned to the secondload lock chamber 106 and the second semi-cylindrical valve 116 isclosed. The second load lock chamber 106 may then be vented and purgedwith a gas such as dry nitrogen prior to unloading the processed wafersand loading new wafers.

Loading and unloading of wafers through the door valves 66, 110typically takes place in a controlled clean room using robots whichminimize contamination of the wafers. The load lock 25 apparatus 40 ispreferably controlled by the microprocessor controller 180 whichcontrols the substrate processing platform 52 as well as othercomponents in the clean room. The load lock apparatus 40 preferably hasthe same input/output devices used for the available load lock chambers12, 14 and can thus replace the available chambers 12, 14 with little orno modification of the microprocessor controller 38 or associatedsoftware. Of course, an existing substrate processing platform can bemodified or a new substrate processing platform can be designed, bypersons skilled in the art, to include a load lock apparatus of thepresent invention using the preceding disclosure.

While the foregoing is directed to the preferred embodiment of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof The scope of theinvention is determined by the claims which follow.

What is claimed is:
 1. A load lock apparatus, comprising: a centralhousing having a wall defining an opening for the passage of a substratethere through connecting the central housing and a substrate processingplatform; two or more load lock housings connected to the centralhousing, wherein a first load lock housing is disposed on an uppersurface of the central housing and a second load lock housing isdisposed on a lower surface of the central housing; a load lock valvedisposed between each load lock housing and the central housing; and twoor more substrate cassette holders, each cassette holder being connectedto a cassette mover, each mover being adapted to transfer eachrespective cassette holder between the central housing and one of theload lock housings.
 2. The apparatus of claim 1, wherein each load lockhousing comprises a door valve.
 3. The apparatus of claim 2, whereineach load lock valve is disposed adjacent an opening between eachrespective load lock housing and the central housing.
 4. The apparatusof claim 3, herein a first load lock valve isolates a first space in thefirst load lock housing from the central housing and a second load lockvalve isolates a second space in the second load lock housing from thecentral housing.
 5. The apparatus of claim 1, wherein each load lockvalve comprises a removable valve seal.
 6. The apparatus of claim 1wherein the two or more substrate cassette holders are configured toreceive multiple substrates.
 7. A load lock apparatus, comprising: acentral housing having a wall defining an opening for the passage of asubstrate there through connecting the central housing and a substrateprocessing platform; two or more load lock housings disposed verticallyon opposing sides of the central housing, wherein a first load lockhousing is disused on an upper surface of the central housing and asecond load lock housing is disposed on a lower surface of the centralhousing; and a load lock valve disposed between each load lock housingand the central housing.
 8. The apparatus of claim 7, wherein each loadlock valve is disposed adjacent an opening between each respective loadlock housing and the central housing.
 9. The apparatus of claim 7,wherein each load lock valve comprises a semi-cylindrical valve.
 10. Theapparatus of claim 7, further comprising: a substrate cassette holder ineach load lock housing collected to a cassette mover and disposable ineach load lock housing.
 11. A load lock apparatus, comprising: a centralhousing having a wall defining an opening for the passage of a substratethere through connecting the central housing and a substrate processingplatform; two or more load lock housings connected to the centralhousing; a semi-cylindrical valve pivotally mounted between each loadlock housing and the central housing; and two or more substrate cassetteholders, each cassette holder being connected to a cassette mover, themover being adapted to transfer each respective cassette holder betweenthe central chamber and one of the load lock chambers.